1. Field of the Invention
The present invention relates to an image signal processing apparatus, a memory control method, and a program for implementing the method, and in particular to an image signal processing apparatus including an image pickup device that outputs an image signal corresponding to a subject, a memory control method applied to the image signal processing apparatus, and a program for causing a computer to execute the memory control method.
For example, the present invention is applied to an image signal processing apparatus that can pickup moving images where during moving image pickup, a display rate of an electronic viewfinder differs to an image recording rate.
2. Description of the Related Art
Conventionally, as an image signal processing apparatus where reading rate for reading from a VRAM (Video Random Access Memory), which is a memory storing image information, to an image display section is faster than writing rate for writing into the VRAM, an apparatus that uses and switches between two VRAMs to prevent “simultaneous display of an original image and the immediately preceding image” has been proposed (see Japanese Laid-Open Patent Publication (Kokai) No. H06-067632). The expression “simultaneous display of an original image and the immediately preceding image” refers to a phenomenon where images picked up at different times are read out to be displayed respectively at upper and lower parts of a screen due to reading of an image signal “overtaking” from a VRAM writing of another image signal into the VRAM during the writing of the latter signal into the VRAM or due to writing of an image signal into a VRAM “overtaking” reading of another image signal from the VRAM during the reading of the latter signal from the VRAM.
Another apparatus has been proposed that prevents writing from overtaking reading and reading from overtaking writing by switching the control method for reading from a VRAM and writing into the VRAM both when the rate of writing into the VRAM is faster than the rate of reading from the VRAM to an image display section and when the rate of reading from the VRAM to the image display section is faster than the ate of writing into the VRAM (see Japanese Laid-Open Patent Publication (Kokai) No. 2003-324644).
Another apparatus has been proposed that changes encoding parameters in accordance with the data amount of images when compressing and recording moving images in parallel with the displaying of images so that images can be stored in real time on a storage medium while appropriately controlling the compressed image data size (see Japanese Laid-Open Patent Publication (Kokai) No. 2000-197003).
However, the apparatuses disclosed in Japanese Laid-Open Patent Publications (Kokai) Nos. H06-067632 and 2003-324644 do not contemplate how to avoid the “simultaneous display of an original image and the immediately preceding image” when moving images are being displayed during the picking up of moving images.
The apparatus disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-197003 records moving images onto a recording medium in real time, and therefore, when the data amount of images suddenly changes, such as when the speed at which images change and/or the resolution of images suddenly change due to a change of scene, for example, a compression circuit cannot achieve a predetermined frame rate, resulting in the problem of frames being dropped during the recording of moving images.